Use of a paraffinic base oil for the reduction of nitrogen oxide emissions

ABSTRACT

The present invention relates to the use of a paraffinic base oil in a lubricant for the reduction of nitrogen oxide emissions of compression ignition engines, wherein the paraffinic base oil comprises (i) a continuous series of iso-paraffins having n, n+1, n+2, n+3 and n+4 carbon atoms, wherein n is between 15 and 40.

FIELD OF INVENTION

The present invention relates to the use of a paraffinic base oil forthe reduction of nitrogen oxide emissions in a combustion engine. Morespecifically, the invention relates to the use of a paraffinic base oilfor use in an internal combustion compression ignition engine.

BACKGROUND OF THE INVENTION

In recent decades, use of internal combustion engines, in particularcompression ignition engines for transportation and other means ofenergy generation has become more and more widespread. Compressionignition engines, which will be referred to further as “Diesel engines”after Rudolf Diesel, who invented the first compression ignition enginein 1892, feature among the main type of engines employed for passengercars in Europe, and globally for heavy duty applications, as well as forstationary power generation as a result of their high efficiency.

A diesel engine is an internal combustion engine; more specifically, itis a compression ignition engine, in which the fuel/air mixture isignited by being compressed until it ignites due to the temperatureincrease due to compression, rather than by a separate source ofignition, such as a spark plug, as is the case of gasoline engines.

The growing spread of Diesel engines has resulted in increasedregulatory pressure with respect to engine emissions; more specificallywith respect to exhaust gases and particulate matter in the exhaust gasstream.

A variety of strategies for controlling and reducing in particularparticulate matter emissions from Diesel engines have been reported inrecent years. These include the use of fuel additives, specific mineraloil derived fuels of low sulphur contents, and/or synthetic fuels, asfor instance described in US-A-20050154240. This document discloses theuse of highly iso-paraffinic based gas oils derived from aFischer-Tropsch process for reducing particulate emission fromcompression ignition engines. Other approaches include the formulationof low sulphur lubricant compositions comprising active compounds suchas acylated nitrogen-containing compounds as disclosed in WO-A-02/24842.Yet other approaches to reduce particulate exhaust emissions havefocused on engine management, more specifically injection and combustionprocesses, as disclosed for instance in U.S. Pat. No. 6,651,614. Thetrend to improved engine management has generally led to highercombustion temperatures, which result in increased formation of nitrogenoxides. Nitrogen oxides (NOx) are demonstrated to be hazardous to bothplant and animal health, and are difficult and slow to convert byfixed-bed catalyst systems, as for instance those described in U.S. Pat.No. 6,696,389, and/or may require further cumbersome and complextreatment, as for instance disclosed in EP-A-1010870.

Hence, there is a need for a further reduction of nitrogen oxides indiesel engine exhaust gases.

It has now surprisingly been found by applicants that by using aspecific lubricant, the amount of nitrogen oxides in the exhaust gasescan be significantly reduced.

SUMMARY OF THE INVENTION

Accordingly, the present invention relates to the use of a lubricantcomposition in a diesel engine, wherein the lubricant comprises a baseoil comprising (i) a series of iso-paraffins having n, n+1, n+2, n+3 andn+4 carbon atoms, wherein n is between 15 and 40.

DETAILED DESCRIPTION OF THE FIGURE

FIG. 1 shows a comparison between four heavy duty diesel test cycles.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to use of a lubricant to lubricate acompression ignition internal combustion engine, i.e. a Diesel Engine, areciprocating engine, rotary engine (also referred to as Wankel engine)and similar designed engine in which combustion is intermittent.

Applicants have found that the use of a lubricant comprising aFischer-Tropsch derived base oil leads to a significant and unexpectedreduction of nitrogen oxide emission of a Diesel engine.

The diesel engine for which the lubricant according to the invention isto be employed is lubricated, i.e. the lubricant forms a film betweensurfaces of parts moving against each other so as to minimize directcontact between them. This lubricating film decreases friction, wearing,and production of excessive heat between the moving parts. Also as amoving fluid, the lubricant transposes heat from surfaces of lubricatedparts due to friction from parts moving against each other or the oilfilm. Typically, a Diesel engine has a crankcase, cylinder head, andcylinders. The lubricant is typically present in the crankcase, wherecrankshaft, bearings, and bottoms of rods connecting pistons to thecrankshaft are coated in the lubricant. The rapid motion of these partscauses the lubricant to splash and lubricate the contacting surfacesbetween the piston rings and interior surfaces of the cylinders. Thislubricant film also serves as a seal between the piston rings andcylinder walls to separate the combustion volume in the cylinders fromthe space in the crankcase. Accordingly, it comprises one or more fuelcomponents that by boiling range and other structure are suitable to actas fuel for compression ignition engines. Generally, such engines employpiston crown lubrication, which is preferred, since hereby the lubricantcontributes to the engine cooling. In such engines, the piston isusually formed as a cast article having a crown portion and a hollowcylindrical sidewall portion, wherein the crown portion is formed with atransverse hollow space, wherein the hollow space is circulated bylubricant for the purpose of cooling the crown portion. Lubricant issupplied to the hollow space by splashing.

Without wishing to be bound to any particular theory, it is believedthat the presence of the residual lubricant film, in synergy with thespecific highly paraffinic fuel reduces the temperature of the pistonand interior surfaces of the cylinder, thereby reducing the formation ofnitrogen oxides.

The fuel composition comprises is suitable for compression ignitionengines. Accordingly, it comprises one or more fuel components that byboiling range and other structure are suitable to act as fuel forcompression ignition engines. The fuel composition thus preferably has acetane number of at least 40, a sulphur content of less than 100 ppm anda flash point of at least 68° C.

The fuel composition according to invention may comprise one or morefuel components, of which preferably one is a paraffinic gas oilcomponent. The fuel may advantageously comprise a mixture of two or moreFischer-Tropsch derived gas oil and/or kerosene fuels, optionally inadmixture with non-Fischer-Tropsch derived gas oils and/or kerosenes.The fuel composition may further comprise additives usually employed infuels. With a paraffinic gas oil component is meant a compositioncomprising more than 80 wt % paraffins, more preferably more than 90 wt% paraffins and even more preferably more than 95 wt % paraffins. Theiso to normal ratio of the paraffins as present in the paraffin fuel ispreferably greater than 0.3, more preferably greater than 1, even morepreferably greater than 3. The paraffin fuel may comprise ofsubstantially only iso-paraffins.

The paraffinic gas oil component preferably comprises a series ofiso-paraffins having n, n+1, n+2, n+3 and n+4 carbon atoms, and whereinn is between 8 and 25. Such paraffinic gas oils are preferably obtainedfrom a Fischer-Tropsch synthesis process, in particular those boiling inthe gas oil and/or kerosene range. Preferably, the paraffinic gas oilcomponent is a Fischer-Tropsch derived gas oil, or a blend thereof.

The fuel composition according to the invention preferably comprises amixture of normal paraffins and iso-paraffins, the normal paraffinspresent in an amount of less than 99% by weight of the fuel composition;and aromatic hydrocarbons present in an amount of less than 10% byweight of the gas oil fuel. Yet more preferably, the paraffinic gas oilcomponent has an iso-paraffin to n-paraffin mass ratio that generallyincreases as paraffin carbon number increases from C8 to C18. Fuelsbased on such paraffinic components showed an improved reduction inexhaust gases in general, and more specifically in nitrogen oxides, whenused in combination with the lubricant according to the invention.

The components of the gas oil component preferably have boiling pointswithin the typical diesel fuel (“gas oil”) range, i.e., from about 150to 400° C. or from 170 to 370° C. It will suitably have a 90% w/wdistillation temperature of from 300 to 370° C.

The gas oil component employed in the fuel composition in accordancewith the present invention preferably further comprises at least 80%w/w, more preferably at least 90% w/w, most preferably at least 95% w/w,of paraffinic components, preferably iso- and linear paraffins. Theweight ratio of iso-paraffins to normal paraffins will suitably begreater than 0.3 and may be up to 12; suitably it is from 2 to 6. By“Fischer-Tropsch derived” is meant that a fuel component or a base oilis, or derives from, a synthesis product of a Fischer-Tropschcondensation process. The term “non-Fischer-Tropsch derived” may beinterpreted accordingly. A Fischer-Tropsch derived fuel may also bereferred to as a GTL (Gas-To-Liquids) fuel. The Fischer-Tropsch reactionconverts carbon monoxide and hydrogen into longer chain, usuallyparaffinic, hydrocarbons:

n(CO+2H₂)═(—CH₂—)_(n) +nH₂O+heat,

in the presence of an appropriate catalyst and typically at elevatedtemperatures (e.g., 125 to 300° C., preferably 175 to 250° C.) and/orpressures (e.g., 5 to 100 bar, preferably 12 to 50 bar). Hydrogen tocarbon monoxide ratios other than 2:1 may be employed if desired. Thecarbon monoxide and hydrogen may themselves be derived from organic orinorganic, natural or synthetic sources, typically either from naturalgas or from organically derived methane.

The actual value for this ratio will be determined, in part, by thehydroconversion process used to prepare the gas oil or fuel componentderived from the Fischer-Tropsch synthesis product. Preferably, theFischer-Tropsch derived gas oil the fuel comprises at least 50% w/w ofiso-paraffins. Some cyclic paraffins may also be present.

Preferably, the Fischer-Tropsch derived gas oil has an average of morethan 1 alkyl branch per paraffinic molecule. Fischer-Tropsch derived gasoils according to the invention as described herein-above may beobtained directly from the Fischer-Tropsch reaction, or indirectly forinstance by fractionation of Fischer-Tropsch synthesis products or fromhydrotreated Fischer-Tropsch synthesis products. Hydrotreatment caninvolve hydrocracking to adjust the boiling range (see, e.g.,GB-B-2077289 and EP-A-0147873) and/or hydroisomerisation which canimprove cold flow properties by increasing the proportion of branchedparaffins. EP-A-0583836 describes a two step hydrotreatment process inwhich a Fischer-Tropsch synthesis product is firstly subjected tohydroconversion under conditions such that it undergoes substantially noisomerisation or hydrocracking (this hydrogenates the olefinic andoxygen-containing components), and then at least part of the resultantproduct is hydroconverted under conditions such that hydrocracking andisomerisation occur to yield a substantially paraffinic hydrocarbonfuel. The desired gas oil fraction(s) may subsequently be isolated forinstance by distillation.

Other post-synthesis treatments, such as polymerisation, alkylation,distillation, cracking-decarboxylation, dewaxing, isomerisation andhydroreforming, may be employed to modify the properties ofFischer-Tropsch condensation products, as described for instance in U.S.Pat. No. 4,125,566 and U.S. Pat. No. 4,478,955. Typical catalysts forthe Fischer-Tropsch synthesis of paraffinic hydrocarbons comprise, asthe catalytically active component, a metal from Group VIII of theperiodic table, in particular ruthenium, iron, cobalt or nickel.Suitable such catalysts are described for instance in EP-A-0583836(pages 3 and 4).

An example of a Fischer-Tropsch based process is the SMDS (Shell MiddleDistillate Synthesis) described in “The Shell Middle DistillateSynthesis Process”, van der Burgt et al (supra). This process (alsosometimes referred to as the Shell “Gas-To-Liquids” or “GTL” technology)produces middle distillate range products by conversion of a natural gas(primarily methane) derived synthesis gas into a heavy long chainhydrocarbon (paraffin) wax which can then be hydroconverted andfractionated to produce liquid transport fuels such as the gas oilsuseable in diesel fuel compositions. A version of the SMDS process,utilising a fixed bed reactor for the catalytic conversion step, iscurrently in use in Bintulu, Malaysia and its gas oil products have beenblended with petroleum derived gas oils in commercially availableautomotive fuels.

Gas oils prepared by the SMDS process are commercially available forinstance from Shell companies.

Further examples of Fischer-Tropsch derived gas oils are described inEP-A-0583836, EP-A-1101813, WO-A-97/14768, WO-A-97/14769, WO-A-00/20534,WO-A-00/20535, WO-A-00/11116, WO-A-00/11117, WO-A-01/83406,WO-A-01/83641, WO-A-01/83647, WO-A-01/83648 and U.S. Pat. No. 6,204,426.

By virtue of the Fischer-Tropsch process, a Fischer-Tropsch derived fuelhas essentially no, or detection limit levels of, sulphur and nitrogen.Compounds containing these heteroatoms tend to act as poisons forFischer-Tropsch catalysts and are therefore removed from the synthesisgas feed. This can yield additional benefits, in terms of effect oncatalyst performance, in fuel compositions in accordance with thepresent invention.

Further, the Fischer-Tropsch process as usually operated produces no orvirtually no aromatic components. The aromatics content of aFischer-Tropsch derived fuel, suitably determined by ASTM D4629, willtypically be below 1% w/w, preferably below 0.5% w/w and more preferablybelow 0.1% w/w.

Generally speaking, Fischer-Tropsch derived fuels have relatively lowlevels of polar components, in particular polar surfactants, forinstance compared to petroleum derived fuels. It is believed that thiscan contribute to improved antifoaming and dehazing performance. Suchpolar components may include for example oxygenates, and sulphur andnitrogen containing compounds. A low level of sulphur in aFischer-Tropsch derived fuel is generally indicative of low levels ofboth oxygenates and nitrogen-containing compounds, since all are removedby the same treatment processes.

As set out above, the fuel may include a mixture of two or moreFischer-Tropsch derived gas oil and kerosene fuels. The components of aFischer-Tropsch derived gas oil (or the majority, for instance 95% w/wor greater, thereof) preferably have boiling points within the typicaldiesel fuel (“gas oil”) range, i.e., from about 150 to 400° C. or from170 to 370° C. The gas oil component will suitably have a 90% w/wdistillation temperature of from 300 to 370° C.

Preferably, the paraffinic gas oil has an iso-paraffin to n-paraffinmass ratio that generally increases as paraffin carbon number increasesfrom C8 to C18, and wherein the fuel comprises less than 0.05% m/msulphur and less than 10% by mass aromatics. Preferably, the gas oil hasan average of more than 1 alkyl branch per paraffinic molecule.Preferably, the fuel comprises at least 50 mass % iso-paraffins.

The paraffinic gas oil will typically have a density from 0.76 to 0.79g/cm³ at 15° C.; a cetane number (ASTM D613) of at least 65, preferablygreater than 70, suitably from 74 to 85; a kinematic viscosity (ASTMD445) from 2 to 4.5, preferably from 2.5 to 4.0, more preferably from2.9 to 3.7, centistokes at 40° C.; and a sulphur content (ASTM D2622) of5 ppmw or less, preferably of 2 ppmw or less.

Preferably, the paraffinic gas oil is a product prepared by aFischer-Tropsch methane condensation reaction using a hydrogen/carbonmonoxide ratio of less than 2.5, preferably less than 1.75, morepreferably from 0.4 to 1.5, and ideally using a cobalt containingcatalyst. It may be obtained from a hydrocracked Fischer-Tropschsynthesis product (for instance as described in GB-B-2077289 and/orEP-A-0147873), or more preferably a product from a two-stagehydroconversion process such as that described in EP-A-0583836 (seeabove). In the latter case, preferred features of the hydroconversionprocess may be as disclosed at pages 4 to 6, and in the examples, ofEP-A-0583836. A fuel composition according to the invention may includea mixture of two or more Fischer-Tropsch derived gas oils. TheFischer-Tropsch derived fuel, and any other fuel component(s) present inthe composition, will suitably all be in liquid form under ambientconditions.

The present invention may be applicable where the fuel composition issuitable for, and/or intended for, use in any system which can bepowered by or otherwise consume a fuel, in particular a diesel fuel,composition. In particular it may be suitable, and/or intended, for usein an internal or external (preferably internal) combustion engine, moreparticularly for use as an automotive fuel and most particularly for usein an internal combustion engine of the compression ignition (diesel)type.

The fuel composition will preferably be, overall, a low or ultra lowsulphur fuel composition, or a sulphur free fuel composition, forinstance containing at most 500 ppmw, preferably no more than 350 ppmw,most preferably no more than 100 or 50 ppmw, or even 10 ppmw or less, ofsulphur.

Where the fuel composition is an automotive diesel fuel composition, itpreferably falls within applicable current standard specification(s)such as for example EN 590:99. It suitably has a density from 0.82 to0.845 g/cm³ at 15° C.; a final boiling point (ASTM D86) of 360° C. orless; a cetane number (ASTM D613) of 51 or greater; a kinematicviscosity (ASTM D445) from 2 to 4.5 centistokes at 40° C.; a sulphurcontent (ASTM D2622) of 350 ppmw or less; and/or a total aromaticscontent (IP 391(mod)) of less than 11.

The fuel composition may also advantageously comprise up to 30% v/v of aFischer-Tropsch derived kerosene fuel. All concentrations, unlessotherwise stated, are quoted as percentages of the overall fuelcomposition. The concentrations of the Fischer-Tropsch derived gas oil,will generally be chosen to ensure that the density, cetane number,calorific value and/or other relevant properties of the overall fuelcomposition are within the desired ranges, for instance withincommercial or regulatory specifications.

The fuel composition employed in the lubricant-and-fuel combinationaccording to the present invention may contain other components inaddition to the non-Fischer-Tropsch derived fuel and the Fischer-Tropschderived fuel components.

The base fuel may itself be additivated (additive-containing) orunadditivated (additive-free). If additivated, it will contain one ormore additives selected for example from anti-static agents, pipelinedrag reducers, flow improvers (e.g. ethylene/vinyl acetate copolymers oracrylate/maleic anhydride copolymers), lubricity additives, antioxidantsand wax anti-settling agents.

Detergent-containing diesel fuel additives are known and commerciallyavailable. Such additives may be added to diesel fuels at levelsintended to reduce, remove, or slow the build up of engine deposits.Examples of detergents suitable for use in fuel additives for thepresent purpose include polyolefin substituted succinimides orsuccinamides of polyamines, for instance polyisobutylene succinimides orpolyisobutylene amine succinamides, aliphatic amines, Mannich bases oramines and polyolefin (e.g. polyisobutylene) maleic anhydrides.Succinimide dispersant additives are described for example inGB-A-960493, EP-A-0147240, EP-A-0482253, EP-A-0613938, EP-A-0557516 andWO-A-98/42808. Particularly preferred are polyolefin substitutedsuccinimides such as polyisobutylene succinimides.

The additive may contain other components in addition to the detergent.Examples are lubricity enhancers; dehazers, e.g. alkoxylated phenolformaldehyde polymers; anti-foaming agents (e.g. polyether-modifiedpolysiloxanes); ignition improvers (cetane improvers) (e.g. 2-ethylhexylnitrate (EHN), cyclohexyl nitrate, di-tert-butyl peroxide and thosedisclosed in U.S. Pat. No. 4,208,190 at column 2, line 27 to column 3,line 21); anti-rust agents (e.g. a propane-1,2-diol semi-ester oftetrapropenyl succinic acid, or polyhydric alcohol esters of a succinicacid derivative, the succinic acid derivative having on at least one ofits alpha-carbon atoms an unsubstituted or substituted aliphatichydrocarbon group containing from 20 to 500 carbon atoms, e.g. thepentaerythritol diester of polyisobutylene-substituted succinic acid);corrosion inhibitors; reodorants; anti-wear additives; anti-oxidants(e.g. phenolics such as 2,6-di-tert-butylphenol, or phenylenediaminessuch as N,N′-di-sec-butyl-p-phenylenediamine); metal deactivators; andcombustion improvers. It is particularly preferred that the additiveinclude a lubricity enhancer, especially when the fuel composition has alow (e.g. 500 ppmw or less) sulphur content. In the additivated fuelcomposition, the lubricity enhancer is conveniently present at aconcentration of less than 1000 ppmw, preferably between 50 and 1000ppmw, more preferably between 100 and 1000 ppmw. Suitable commerciallyavailable lubricity enhancers include ester- and acid-based additives.Other lubricity enhancers are described in the patent literature, inparticular in connection with their use in low sulphur content dieselfuels, for example in:

the paper by Danping Wei and H. A. Spikes, “The Lubricity of DieselFuels”, Wear, III (1986) 217-235;

WO-A-95/33805—cold flow improvers to enhance lubricity of low sulphurfuels;

WO-A-94/17160—certain esters of a carboxylic acid and an alcohol whereinthe acid has from 2 to 50 carbon atoms and the alcohol has 1 or morecarbon atoms, particularly glycerol monooleate and di-isodecyl adipate,as fuel additives for wear reduction in a diesel engine injectionsystem;

U.S. Pat. No. 5,490,864—certain dithiophosphoric diester-dialcohols asanti-wear lubricity additives for low sulphur diesel fuels; and.

WO-A-98/01516—certain alkyl aromatic compounds having at least onecarboxyl group attached to their aromatic nuclei, to confer anti-wearlubricity effects particularly in low sulphur diesel fuels.

It is also preferred that the additive contain an anti-foaming agent,more preferably in combination with an anti-rust agent and/or acorrosion inhibitor and/or a lubricity additive.

Unless otherwise stated, the (active matter) concentration of each suchadditional component in the additivated fuel composition is preferablyup to 10000 ppmw, more preferably in the range from 0.1 to 1000 ppmw,advantageously from 0.1 to 300 ppmw, such as from 0.1 to 150 ppmw.

The (active matter) concentration of any dehazer in the fuel compositionwill preferably be in the range from 0.1 to 20 ppmw, more preferablyfrom 1 to 15 ppmw, still more preferably from 1 to 10 ppmw,advantageously from 1 to 5 ppmw. The (active matter) concentration ofany ignition improver present will preferably be 2600 ppmw or less, morepreferably 2000 ppmw or less, conveniently from 300 to 1500 ppmw.

If desired, the additive components, as listed above, may be co-mixed,preferably together with suitable diluent(s), in an additiveconcentrate, and the additive concentrate may be dispersed into thefuel, in suitable quantity to result in a composition of the presentinvention.

In the case of a diesel fuel composition, for example, the additive willtypically contain a detergent, optionally together with other componentsas described above, and a diesel fuel-compatible diluent, which may be acarrier oil (e.g. a mineral oil), a polyether, which may be capped oruncapped, a non-polar solvent such as toluene, xylene, white spirits andthose sold by Shell companies under the trade mark “SHELLSOL”, and/or apolar solvent such as an ester and, in particular, an alcohol, e.g.hexanol, 2-ethylhexanol, decanol, isotridecanol and alcohol mixturessuch as those sold by Shell companies under the trade mark “LINEVOL”,especially LINEVOL 79 alcohol which is a mixture of C₇₋₉ primaryalcohols, or a C₁₂₋₁₄ alcohol mixture which is commercially available.The total content of the additives may be suitably between 0 and 10000ppmw and preferably below 5000 ppmw.

The lubricant according to the invention preferably comprises at leastone base oil having a paraffin content of greater than 80 wt % paraffinsand a saturates content of greater than 98 wt % and comprising acontinuous series of iso-paraffins having n, n+1, n+2, n+3 and n+4carbon atoms. The base oil preferably is a Fischer-Tropsch derived baseoil, having a paraffin content of greater than 80 wt % paraffins, asaturates content of greater than 98 wt % and comprises a continuousseries of iso-paraffins having n, n+1, n+2, n+3 and n+4 carbon atoms,wherein n is between 15 and 40. In the case of the Fischer-Tropschderived base oil, the base oil contains a continuous series of theseries of iso-paraffins having n, n+1, n+2, n+3 and n+4 carbon atoms.The content and the presence of the a continuous series of the series ofiso-paraffins having n, n+1, n+2, n+3 and n+4 carbon atoms in the baseoil or base stock (i) may be measured by Field desorption/FieldIonisation (FD/FI) technique. In this technique the oil sample is firstseparated into a polar (aromatic) phase and a non-polar (saturates)phase by making use of a high performance liquid chromatography (HPLC)method IP368/01, wherein as mobile phase pentane is used instead ofhexane as the method states. The saturates and aromatic fractions arethen analyzed using a Finnigan MAT90 mass spectrometer equipped with aField desorption/Field Ionisation (FD/FI) interface, wherein FI (a“soft” ionisation technique) is used for the determination ofhydrocarbon types in terms of carbon number and hydrogen deficiency. Thetype classification of compounds in mass spectrometry is determined bythe characteristic ions formed and is normally classified by “z number”.This is given by the general formula for all hydrocarbon species:C_(n)H_(2n+z). Because the saturates phase is analysed separately fromthe aromatic phase it is possible to determine the content of thedifferent iso-paraffins having the same stoichiometry or n-number. Theresults of the mass spectrometer are processed using commercial software(poly 32; available from Sierra Analytics LLC, 3453 Dragoo Park Drive,Modesto, Calif. GA95350 USA) to determine the relative proportions ofeach hydrocarbon type.

The base oil containing a continuous iso-paraffinic series as describedabove is obtained by hydroisomerisation of a paraffinic wax, preferablyfollowed by some type of dewaxing, such as solvent or catalyticdewaxing. The paraffinic wax is a Fischer-Tropsch derived wax.

The base oils as derived from a Fischer-Tropsch wax as here describedwill be referred to in this description as Fischer-Tropsch derived baseoils. Examples of Fischer-Tropsch processes which for example can beused to prepare the above-described Fischer-Tropsch derived base oil arethe so-called commercial Slurry Phase Distillate technology of Sasol,the Shell Middle Distillate Synthesis Process and the “AGC-21” ExxonMobil process. These and other processes are for example described inmore detail in EP-A-776959, EP-A-668342, U.S. Pat. No. 4,943,672, U.S.Pat. No. 5,059,299, WO-A-9934917 and WO-A-9920720. Typically theseFischer-Tropsch synthesis products will comprise hydrocarbons having 1to 100 and even more than 100 carbon atoms. This hydrocarbon productwill comprise normal paraffins, iso-paraffins, oxygenated products andunsaturated products. If base oils are one of the desired iso-paraffinicproducts it may be advantageous to use a relatively heavyFischer-Tropsch derived feed. The relatively heavy Fischer-Tropschderived feed has at least 30 wt %, preferably at least 50 wt %, and morepreferably at least 55 wt % of compounds having at least 30 carbonatoms. Furthermore the weight ratio of compounds having at least 60 ormore carbon atoms and compounds having at least 30 carbon atoms of theFischer-Tropsch derived feed is preferably at least 0.2, more preferablyat least 0.4 and most preferably at least 0.55. Preferably theFischer-Tropsch derived feed comprises a C₂₀+ fraction having anASF-alpha value (Anderson-Schulz-Flory chain growth factor) of at least0.925, preferably at least 0.935, more preferably at least 0.945, evenmore preferably at least 0.955. Such a Fischer-Tropsch derived feed canbe obtained by any process, which yields a relatively heavyFischer-Tropsch product as described above. Not all Fischer-Tropschprocesses yield such a heavy product. An example of a suitableFischer-Tropsch process is described in WO-A-9934917. TheFischer-Tropsch derived base oil will contain no or very little sulphurand nitrogen containing compounds. This is typical for a product derivedfrom a Fischer-Tropsch reaction, which uses synthesis gas containingalmost no impurities. Sulphur and nitrogen levels will generally bebelow the detection limits, which are currently 5 mg/kg for sulphur and1 mg/kg for nitrogen respectively.

The process will generally comprise a Fischer-Tropsch synthesis, ahydroisomerisation step and an optional pour point reducing step,wherein said hydroisomerisation step and optional pour point reducingstep are performed as: (a) hydrocracking/hydroisomerisating aFischer-Tropsch product, (b) separating the product of step (a) into atleast one or more distillate fuel fractions and a base oil or base oilintermediate fraction.

If the viscosity and pour point of the base oil as obtained in step (b)is as desired no further processing is necessary and the oil can be usedas the base oil according the invention. If required, the pour point ofthe base oil intermediate fraction is suitably further reduced in a step(c) by means of solvent or preferably catalytic dewaxing of the oilobtained in step (b) to obtain oil having the preferred low pour point.The desired viscosity of the base oil may be obtained by isolating bymeans of distillation from the intermediate base oil fraction or fromthe dewaxed oil the suitable boiling range product corresponding withthe desired viscosity. Distillation may be suitably a vacuumdistillation step.

The hydroconversion/hydroisomerisation reaction of step (a) ispreferably performed in the presence of hydrogen and a catalyst, whichcatalyst can be chosen from those known to one skilled in the art asbeing suitable for this reaction of which some will be described in moredetail below. The catalyst may in principle be any catalyst known in theart to be suitable for isomerising paraffinic molecules. In general,suitable hydroconversion/hydroisomerisation catalysts are thosecomprising a hydrogenation component supported on a refractory oxidecarrier, such as amorphous silica-alumina (ASA), alumina, fluoridedalumina, molecular sieves (zeolites) or mixtures of two or more ofthese. One type of preferred catalysts to be applied in thehydroconversion/hydroisomerisation step in accordance with the presentinvention are hydroconversion/hydroisomerisation catalysts comprisingplatinum and/or palladium as the hydrogenation component. A very muchpreferred hydroconversion/hydroisomerisation catalyst comprises platinumand palladium supported on an amorphous silica-alumina (ASA) carrier.The platinum and/or palladium is suitably present in an amount of from0.1 to 5.0% by weight, more suitably from 0.2 to 2.0% by weight,calculated as element and based on total weight of carrier. If bothpresent, the weight ratio of platinum to palladium may vary within widelimits, but suitably is in the range of from 0.05 to 10, more suitably0.1 to 5. Examples of suitable noble metal on ASA catalysts are, forinstance, disclosed in WO-A-9410264 and EP-A-0582347. Other suitablenoble metal-based catalysts, such as platinum on a fluorided aluminacarrier, are disclosed in e.g. U.S. Pat. No. 5,059,299 and WO-A-9220759.A second type of suitable hydroconversion/hydroisomerisation catalystsare those comprising at least one Group VIB metal, preferably tungstenand/or molybdenum, and at least one non-noble Group VIII metal,preferably nickel and/or cobalt, as the hydrogenation component. Bothmetals may be present as oxides, sulphides or a combination thereof. TheGroup VIB metal is suitably present in an amount of from 1 to 35% byweight, more suitably from 5 to 30% by weight, calculated as element andbased on total weight of the carrier. The non-noble Group VIII metal issuitably present in an amount of from 1 to 25 wt %, preferably 2 to 15wt %, calculated as element and based on total weight of carrier. Ahydroconversion catalyst of this type, which has been found particularlysuitable, is a catalyst comprising nickel and tungsten supported onfluorided alumina.

The above non-noble metal-based catalysts are preferably used in theirsulphided form. In order to maintain the sulphided form of the catalystduring use some sulphur needs to be present in the feed. Preferably atleast 10 mg/kg and more preferably between 50 and 150 mg/kg of sulphuris present in the feed.

A preferred catalyst, which can be used in a non-sulphided form,comprises a non-noble Group VIII metal, e.g., iron, nickel, inconjunction with a Group IB metal, e.g., copper, supported on an acidicsupport. Copper is preferably present to suppress hydrogenolysis ofparaffins to methane. The catalyst has a pore volume preferably in therange of 0.35 to 1.10 ml/g as determined by water absorption, a surfacearea of preferably between 200-500 m²/g as determined by BET nitrogenadsorption, and a bulk density of between 0.4-1.0 g/ml. The catalystsupport is preferably made of an amorphous silica-alumina wherein thealumina may be present within wide range of between 5 and 96 wt %,preferably between 20 and 85 wt %. The silica content as SiO₂ ispreferably between 15 and 80 wt %. Also, the support may contain smallamounts, e.g., 20-30 wt %, of a binder, e.g., alumina, silica, Group IVAmetal oxides, and various types of clays, magnesia, etc., preferablyalumina or silica. The preparation of amorphous silica-aluminamicrospheres has been described in Ryland, Lloyd B., Tamele, M. W., andWilson, J. N., Cracking Catalysts, Catalysis: volume VII, Ed. Paul H.Emmett, Reinhold Publishing Corporation, New York, 1960, pp. 5-9.

The catalyst is prepared by co-impregnating the metals from solutionsonto the support, drying at 100-150° C., and calcining in air at200-550° C. The Group VIII metal is present in amounts of about 15 wt %or less, preferably 1-12 wt %, while the Group IB metal is usuallypresent in lesser amounts, e.g., 1:2 to about 1:20 weight ratiorespecting the Group VIII metal.

A typical catalyst is shown below:

Ni, wt % 2.5-3.5 Cu, wt % 0.25-0.35 Al₂O₃—SiO₂ wt % 65-75 Al₂O₃ (binder)wt % 25-30 Surface Area 290-325 m²/g Pore Volume (Hg) 0.35-0.45 ml/gBulk Density 0.58-0.68 g/ml

Another class of suitable hydroconversion/hydroisomerisation catalystsare those based on molecular sieve type materials, suitably comprisingat least one Group VIII metal component, preferably Pt and/or Pd, as thehydrogenation component. Suitable zeolitic and other aluminosilicatematerials, then, include Zeolite beta, Zeolite Y, Ultra Stable Y, ZSM-5,ZSM-12, ZSM-22, ZSM-23, ZSM-48, MCM-68, ZSM-35, SSZ-32, ferrierite,mordenite and silica-aluminophosphates, such as SAPO-11 and SAPO-31.Examples of suitable hydroisomerisation/hydroisomerisation catalystsare, for instance, described in WO-A-9201657. Combinations of thesecatalysts are also possible. Very suitablehydroconversion/hydroisomerisation processes are those involving a firststep wherein a zeolite beta or ZSM-48 based catalyst is used and asecond step wherein a ZSM-5, ZSM-12, ZSM-22, ZSM-23, ZSM-48, MCM-68,ZSM-35, SSZ-32, ferrierite, mordenite based catalyst is used. Of thelatter group ZSM-23, ZSM-22 and ZSM-48 are preferred. Examples of suchprocesses are described in US-A-20040065581, which disclose a processcomprising a first step catalyst comprising platinum and zeolite betaand a second step catalyst comprising platinum and ZSM-48. Theseprocesses are capable of yielding a base oil product which does notrequire a further dewaxing step.

Combinations wherein the Fischer-Tropsch product is first subjected to afirst hydroisomerisation step using the amorphous catalyst comprising asilica-alumina carrier as described above followed by a secondhydroisomerisation step using the catalyst comprising the molecularsieve has also been identified as a preferred process to prepare thebase oil to be used in the present invention. More preferred the firstand second hydroisomerisation steps are performed in series flow. Mostpreferred the two steps are performed in a single reactor comprisingbeds of the above amorphous and/or crystalline catalyst.

In step (a) the feed is contacted with hydrogen in the presence of thecatalyst at elevated temperature and pressure. The temperaturestypically will be in the range of from 175 to 380° C., preferably higherthan 250° C. and more preferably from 300 to 370° C. The pressure willtypically be in the range of from 10 to 250 bar and preferably between20 and 80 bar. Hydrogen may be supplied at a gas hourly space velocityof from 100 to 10000 Nl/l/hr, preferably from 500 to 5000 Nl/l/hr. Thehydrocarbon feed may be provided at a weight hourly space velocity offrom 0.1 to 5 kg/l/hr, preferably higher than 0.5 kg/l/hr and morepreferably lower than 2 kg/l/hr. The ratio of hydrogen to hydrocarbonfeed may range from 100 to 5000 Nl/kg and is preferably from 250 to 2500Nl/kg.

The conversion in step (a) is defined as the weight percentage of thefeed boiling above 370° C. which reacts per pass to a fraction boilingbelow 370° C., is at least 20 wt %, preferably at least 25 wt %, butpreferably not more than 80 wt %, more preferably not more than 65 wt %.The feed as used above in the definition is the total hydrocarbon feedfed to step (a), thus also any optional recycle of a high boilingfraction which may be obtained in step (b).

In step (b) the product of step (a) is preferably separated into one ormore distillate fuels fractions and a base oil or base oil precursorfraction having the desired viscosity properties. If the pour point isnot in the desired range the pour point of the base oil is furtherreduced by means of a dewaxing step (c), preferably by catalyticdewaxing. In such an embodiment it may be a further advantage to dewax awider boiling fraction of the product of step (a). From the resultingdewaxed product the base oil and oils having a desired viscosity canthen be advantageously isolated by means of distillation. Dewaxing ispreferably performed by catalytic dewaxing as for example described inWO-A-02070629, which publication is hereby incorporated by reference.The final boiling point of the feed to the dewaxing step (c) may be thefinal boiling point of the product of step (a) or lower if desired.

The base oil component according to the invention suitably has akinematic viscosity at 100° C. of from 1 to 25 mm²/sec. Preferably, ithas a kinematic viscosity at 100° C. of from 2 to 15 mm²/sec, morepreferably of from 2.5 to 8.5 mm²/sec, yet more preferably from 2.75 to5.5 mm²/sec.

Obviously, a mixture of one or more paraffinic base oils according tothe invention, and of additional base oils may be employed as well. Thelubricant formulation preferably comprises at least 25% wt. of one ormore of the paraffinic base oils, more preferably at least 30% wt., yetmore preferably at least 50% wt., and most preferably at least 70% wt.of the paraffinic base oils.

The lubricant composition preferably contains less than 50% v/v of amineral derived base fuel, more preferably less than 30% v/v, yet morepreferably less than 25% v/v, less than 20% v/v, yet more preferablyless than 15% v/v, again more preferably less than 10% v/v, yet morepreferably less than 8% v/v, again yet more preferably less than 5% v/v,and most preferably less than 2% v/v of a mineral-derived base oil.

The pour point of the base oil is preferably below −30° C.

The flash point of the base oil as measured by ASTM D92 preferably isgreater than 120° C., more preferably even greater than 140° C.

The lubricant for use according to the invention preferably has aviscosity index in the range of from 100 to 600, more preferably aviscosity index in the range of from 110 to 200, and even morepreferably a viscosity index in the range of from 120 to 150.

The lubricant for use according to the invention may comprise as thebase oil component exclusively the paraffinic base oil, or a combinationof the paraffinic base oils and ester as described above, oralternatively in combination with another additional base oil. Theadditional base oil will suitably comprise less than 20 wt %, morepreferably less than 10 wt %, again more preferably less than 5 wt % ofthe total fluid formulation. Examples of such base oils are mineralbased paraffinic and naphthenic type base oils and synthetic base oils,for example poly alkylene glycols and the like. Alternatively, howeverless preferred due to the high costs involved for its preparation, theparaffinic base oil to be employed in the lubricant may also contain afurther base oil. Preferably, this other base oil has a paraffin contentof greater than 80 wt % paraffins and a saturates content of greaterthan 98 wt % and comprises a series of iso-paraffins having n, n+2 andn+4 carbon atoms, however not comprising n+1, and n+3, wherein n isbetween 15 and 40. Yet more preferably, such a base oil is a poly alphaolefin (PAO) derived base oil. Preferably, such a base oil is ahydrogenated polyalpha-olefin (PAO) homopolymerpolymer, i.e. an alphaolefin (PAO) derived base oil, generally classified as API Group IV baseoil. More preferably, the PAO base oil has the composition comprisingthe hydrogenated dimmer, trimer, tetramer, pentamer, and hexamer of analpha-olefin, such as 1-decene, 1-dodecene, or blends thereof.

Poly-alpha-olefins (PAO) are hydrocarbon blends suitable as syntheticbase oils produced by the oligomerization of alpha-olefins or 1-alkenes.PAO is manufactured by oligomerization of a linear alpha olefin followedby hydrogenation to remove unsaturated moieties and fractionation toobtain the desired product slate. 1-decene is the most commonly usedalpha olefin in the manufacture of PAO, but 1-octene, 1-dodecene and1-tetradecene can also be used. PAO's are commonly categorized by thenumbers denoting the approximate viscosity in centistokes of the PAO at100° C. It is known that PAO 2, PAO 2.5, PAO 4, PAO 5, PAO 6, PAO 7, PAO8, PAO 9 and PAO 10 and combinations thereof can be used in engine oils.The higher the viscosity, the longer the average chain length of thepolyalphaolefin. The isomer distribution of a polyalphaolefin used willdepend on the application. A typical polyalphaolefin prepared from1-decene contains predominantly the trimer (C₃₀-hydrocarbons) with muchsmaller amounts of dimer, tetramer, pentamer, and hexamer. While1-decene is the most common starting material, other alphaolefins can beused, depending on the needs of the product oil.

The PAO oil contains a large number of isomers (e.g., the trimer of1-decene contains many C₃₀ isomers, the tetramer contains many C₄₀isomers) which result from skeletal branching during the oligomerization(Shubkin 1993). The most common of these are PAO 4, PAO 6 and PAO 8.Lubricant formulations comprising such PAO base oils have been describedin Kirk-Othmer Encyclopedia of Chemical Technology, 3rd ed., 14,477-526; U.S. Pat. No. 4,218,330 and EP-A-1051466.

The amounts of these additional base oils are limited by the nitrogenoxide reduction that is to be attained. Preferably, the lubricantfurther comprises saturated cyclic hydrocarbons in an amount of from 5to 10% by weight, based on the total lubricant since this improves thelow temperature compatibility of the different components in thelubricant.

The lubricant for use according to the invention further preferablycomprises a viscosity improver in an amount of from 0.01 to 30% byweight. Viscosity index improvers (also known as VI improvers, viscositymodifiers, or viscosity improvers) provide lubricants with high- andlow-temperature operability. These additives impart acceptable viscosityat low temperatures and are preferably shear stable. The lubricant usedin the package according to the invention further preferably comprisesat least one other additional lubricant component in effective amounts,such as for instance polar and/or non-polar lubricant base oils, andperformance additives such as for example, but not limited to, metallicand ashless oxidation inhibitors, ashless dispersants, metallic andashless detergents, corrosion and rust inhibitors, metal deactivators,metallic and non-metallic, low-ash, phosphorus-containing andnon-phosphorus, sulphur-containing and non-sulphur-containing anti-wearagents, metallic and non-metallic, phosphorus-containing andnon-phosphorus, sulphur-containing and non-sulphurous extreme pressureadditives, anti-seizure agents, pour point depressants, wax modifiers,viscosity modifiers, seal compatibility agents, friction modifiers,lubricity agents, anti-staining agents, chromophoric agents, antifoaming agents, demulsifiers, and other usually employed additivepackages. For a review of many commonly used additives, reference ismade to D. Klamann in Lubricants and Related Products, Verlag Chemie,Deerfield Beach, Fla.; ISBN 0-89573-177-0, and to “Lubricant Additives”by M. W. Ranney, published by Noyes Data Corporation of Parkridge, N.J.(1973).

The use of the lubricants according to the invention surprisinglyresulted in engines producing less nitrogen oxides as compared torunning on mineral oil-based lubricants, independently whether the fuelwas a Fischer-Tropsch derived Diesel fuel.

Furthermore, it was found that the base oils, when formulated into anover-based lubricant, did result in a slower decrease of the total base(TBN) number, and a slower increase in the total acid number (TAN) dueto the high oxidative stability of the base oils employed. However, itas also observed that the decrease in TBN was disproportionally lowerthan the increase in TAN, which indicates that less NOx production mightresult in lower amounts of nitric and nitrous acid being formed in thelubricant. This may advantageously be employed for increasing the oilchange intervals, since an unacceptable acidity of the lubricant will bereached at a much later date in continuous use.

The invention will be further illustrated by the following, non-limitingexamples:

Fuel Compositions

Two automotive gas oil compositions were prepared: A Fischer-Tropschautomotive gas oil (F-T AGO) blend consisted of a base fuel (SO40990)with 250 mg/kg R655 lubricity improver and STADIS 450 anti-staticadditive. The conventional automotive gas oil (mineral AGO) was a 50 ppmsulphur fuel meeting European EN590 specification. The fuel code wasDK1703. The composition of the two fuels is depicted in Table 1:

TABLE 1 Comparative Fuel property Test method F1 F2 Density @ 15° IP365/ 0.7846 0.8326 C. (g/cm³) ASTM D4052 Distillation IP 123/ ASTM D86IBP (° C.) 219.5 169.0 10% 245.9 209.0 20% 258.8 231.0 30% 270.1 249.040% 282.5 262.5 50% 295.2 274.5 60% 307.2 285.5 70% 317.7 296.5 80%328.1 309.0 90% 342.1 327.0 95% 353 342.0 FBP 358.2 357.0 Cetane numberASTM D613 79 54.8 Kinematic IP 71/ 3.497 2,895 viscosity @ ASTM D445 40°C. (centistokes) (mm²/s) Cloud point DIN EN 23015 −0.5 −11 (° C.)Sulphur ASTM D2622 <5 49 (WDXRF) (ppmw)

The gas oil fuel F1 had been obtained from a Fischer-Tropsch (SMDS)synthesis product via a two-stage hydroconversion process analogous tothat described in EP-A-0583836. The comparative fuel was a conventional,mineral-oil derived low-sulfur automotive gas oil.

Lubricants

Two lubricant formulations were prepared. For purposes of this test, thebase oils employed in the lubricant compositions were API Gp III baseoils:

A first base oil (BO1) is a fully (100%) Fischer-Tropsch derived baseoil using a Fischer-Tropsch waxy raffinate obtained from Shell SMDSBintulu (Bintulu, Malaysia) as feed. This feed has been subject to asolvent de-waxing step, and had a kinematic viscosity at 100° C. of 5.0cSt. For comparison, a blend (BO2) of two mineral-derived base oilsderived from a hydrowax feedstock (also known as fuel hydrocrackerbottoms), of the YuBase Gp III slate was employed, specifically YuBase 4(BO2 component 1) and YuBase 6 (BO2 component 2, both commerciallyavailable from SK Base Oils, Ulsan, Korea). The blend had a kinematicviscosity at 100° C. of 5.0 cSt.

Both BO1 and BO2 were formulated into a lubricant with a commerciallyavailable additive package. The formulations are based on currentcommercial 5W-40 API-CH4 medium ash heavy duty diesel engine oils, seeTable 2.

The Fischer-Tropsch base oil blend was comparable with the YuBase blendin terms of Vk100C and cold crank viscosity (VdCCS) at −30° C. TheFischer-Tropsch base oil was slightly lower in Noack volatility eventhough its kinematic viscosity at 100° C. (VK100° C.) and its VdCCS wasmarginally lower than the YuBase analogue.

TABLE 2 5W-40 heavy duty diesel engine lubricant characteristicsComparative Component LB1 LB BO1 (F-T) 74.41 — BO2 — 63 component 1 BO2— 11 component 2 Additive 13.0 13.0 package 1 Additive 0.6 0.6 package 2Pour point 0.2 0.2 depressant Antioxidant 0.5 0.5 Viscosity 11.29 11.7modifier Kinematic 14.46 14.27 viscosity at 100° C. [Cst] CCS at −30°65.17 61.23 C. [poise]

The above lubricants and fuels compositions were employed to lubricateand to operate, respectively, an automotive heavy duty engine (Table 3):

TABLE 3 Engine specification and nominal performance data Model: MANTG-A410A Engine: MAN D2866 LF28 six-cylinder DI diesel with exhaust gasrecirculation (EGR) Cylinders: six in-line Bore/Stroke: 128 × 155 mmCapacity: 11.97 litres Maximum Power: 403 hp (301 kW) at 1,900 rpmMaximum Torque: 1,850 Nm (1,363 lbft) between 900-1,300 rpmTransmission: ZF 16-speed direct drive with range-change, splitter andMAN Comfort Shift

The Nitrogen oxide emissions were measured.

Nitrogen Oxide Emissions Data for MAN Euro 3 Heavy Duty Engine

FIG. 1 shows a simple comparison of the measured NOx emissions afterboth pre-degreening of the lubricant oil for 15 hours and a further 85hours of running the engine i.e. 100 hours total running time.(De-greening is a process of stabilisation of the lubricant where theadditive anti-wear components are partially decomposed and laid down onmetal surfaces and the most volatile light ends of base oil evaporate).The 13-mode European Stationary Cycle (ESC) was chosen as the basis forboth mileage accumulation and emissions testing. In this test, theengine is tested on an engine dynamometer over a sequence ofsteady-state modes at equal power delivery. The engine is operated for aprescribed time in each mode, completing engine speed and load changesin the first 20 seconds. The specified speed is held to within 50 rpmand the specified torque is held to within ±2% of the maximum torque atthe test speed. Emissions are measured during each mode and averagedover the cycle using a set of weighting factors. Particulate matteremissions are sampled on one filter over the 13 modes. The finalemission results are expressed in g/kW hr.

It can be seen in FIG. 1 a reduction in NOx emission is obtained whenusing a paraffinic (Fischer-Tropsch derived) gas oil as fuel compared tomineral low Sulphur diesel gas oil for a constant lubricant formulation.This holds respectively for both the paraffinic lubricant formulationaccording to the invention, as well as for the comparativemineral-derived Gp III base oil type formulation.

For the stabilised lubricant after a total of 100 hours engine runningtime it was unexpectedly noticed that the Fischer-Tropsch-base lubricantgave a significantly lower NOx emission than a mineral Gp III base oilbased lubricant, when a simple and absolute comparison of the NOxemissions in units of grams/kilowatt hour (g/kW hr) of engine poweroutput was made. After allowing for effects such as fuel consumptiondifferences (as monitored through carbon dioxide emission), thecombination of the paraffinic base oil according to the invention in thelubricant together with a paraffinic fuel according to the inventionresulted in an unexpectedly synergistic, and non-linear large reductionof the nitrogen oxide emission per unit of carbon dioxide formed ascompared to the paraffinic base oil in the lubricant combined with amineral oil derived fuel, or the combination of a mineral-derived baseoil in the lubricant with a paraffinic, Fischer-Tropsch derivedautomotive gas oil, as illustrated by Table 4.

TABLE 4 Values for the NOx reduction after allowing for related fuelconsumption delta ratio of % NOx delta NOx delta fuel fuel benefit over% Measured emissions delta NOx consumption cons. difference in fuelExperiment effect [g/kW hr] benefit [%] [g/kW hr] [%] consumption A.Mineral Change 0.60 9 30.1 4.3 2.01 Gp III from base oil mineral(constant) gas oil to Fischer- Tropsch gas oil B. Change 0.53 11 27.03.9 2.86 Fischer- from Tropsch Gp mineral III base gas oil to oilFischer- (constant) Tropsch gas oil C. Mineral Change 0.26 5.2 7.73 1.14.66 gas oil from (constant) mineral Gp III base oil to Fischer- TropschGp III base oil D. Change 0.19 4.3 4.70 0.7 6.14 Fischer- from Tropschmineral Gp gas oil III base (constant) oil to Fischer- Tropsch Gp IIIbase oilTable 4 illustrates that there are two effects visible: A first effectis expressed by the change from a mineral gas oil to a Fischer-Tropschderived gas oil at a constant base oil lubricant is in the same range; asecond effect becomes visible when at a constant gas oil, the lubricantcompositions are exchanged. Experiments A and B illustrate thebeneficial effect of the Fischer-Tropsch derived gas oil on the NOxemission.

Experiments C and D illustrate the benefit of the Fischer-Tropschderived base oil in a higher reduction of Nitrogen oxides, and also thehigher effect of the combination of it with a Fischer-Tropsch derivedgas oil. Furthermore, the combination of a Fischer-Tropsch gas oil and aFischer-Tropsch base oil shows a higher reduction of Nitrogen oxidesthan the individual effects of either changing the base oil, or changingthe fuel separately. Yet further, it was found that upon prolongedapplication, the NOx emission benefit with the use of the combinationaccording to the invention was maintained at the same level, while theemissions for the mineral oil derived lubricant formulation increasedover time.

1. A process comprising using a paraffinic base oil in a lubricant forthe reduction of nitrogen oxide emissions of compression ignitionengines, comprising using a paraffinic base oil in a lubricant whereinthe paraffinic base oil comprises (i) a continuous series ofiso-paraffins having n, n+1, n+2, n+3 and n+4 carbon atoms, wherein n isbetween 15 and
 40. 2. A process according to claim 1, wherein theparaffinic base oil is a Fischer-Tropsch derived base oil.
 3. A processaccording to claim 1, wherein the paraffinic base oil has a kinematicviscosity at 100° C. of from 3 to 25 mm²/s.
 4. A process according toclaim 1, wherein the lubricant comprises at least 30% wt. of theparaffinic base oil.
 5. A process according to claim 1, wherein thelubricant comprises less than 50% v/v of a mineral-derived base oil. 6.A process according to claim 1, wherein the fuel comprises aFischer-Tropsch derived gas oil.
 7. A process comprising using aparaffinic base oil in the lubricant for the reduction of increase offormation of nitric and nitrous acid in the lubricant comprising using aparaffinic base oil in the lubricant in a compression ignition engine,wherein the paraffinic base oil comprises (i) a continuous series ofiso-paraffins having n, n+1, n+2, n+3 and n+4 carbon atoms, and whereinn is between 15 and
 40. 8. A process for power generation with reducedexhaust nitrogen oxide gas emission, comprising operating a dieselengine and lubricating the engine with a lubricating oil composition,and wherein the lubricant composition comprises a base oil or base stockhaving a paraffin content of greater than 80 wt % paraffins and asaturates content of greater than 98 wt % and comprising (i) a series ofiso-paraffins having n, n+1, n+2, n+3 and n+4 carbon atoms and wherein nis between 15 and 40.